1. Field of the Invention
The present invention relates to a micro electro discharge machining method and apparatus. The invention more particularly relates to a micro electro discharge machining method and apparatus used in machining parts to be provided with a large number of minute holes having a highly precise shape and a diameter, for example, as small as 100 xcexcm or less such as an ink jet printer nozzle and a suction nozzle for minute parts.
2. Description of Related Art
Minute hole machining includes various methods such as etching by photolithography, laser machining, and electroforming. Among the methods, micro electro discharge machining is suitable for high precision minute hole machining. According to the method, a highly precisely shaped, micro tool electrode is rotated and holes are formed on a one-hole basis by discharge. (Reference: xe2x80x9cMicro Electro Discharge Machining Technologiesxe2x80x9d, National Technical Report, Vol. 39, No. 5, Oct. 1993, pp. 33 to 39).
In the micro electro discharge machining, when a group of a large number of identical size minute holes are formed, the relative position of the tool electrode and a work piece is determined by NC, and holes are sequentially machined on a one-hole basis. When groups of holes having different sizes are formed, tool electrodes corresponding to the hole diameters are prepared and switched during machining.
The described conventional method however suffers from large errors in the size and shape of holes when a large number of minute holes are produced. For example, errors in the process of machining each hole, errors associated with consumption of an electrode in the sequential machining process and errors resulting from the necessity of re-shaping the electrode for its consumption amount to the large errors. In addition, the time for machining increases in proportion to the number of holes to be machined, which impedes improvement in the productivity.
The present invention is directed to a solution to the above disadvantages associated with the conventional method. It is an object of the present invention to provide a micro electro discharge machining method and apparatus which improves the hole size precision at the time of producing a large number of minute holes and shortens the total machining time to improve the productivity.
In a micro electro discharge machining method according to the invention, the relative distance between a tool electrode and a workpiece is changed at a frequency and in an amplitude as desired. Discharge pulse output is controlled in synchronization with the change in the relative distance between the tool electrode and the workpiece to perform electro discharge machining between them.
Electric discharges are caused between a tool electrode and a plate electrode provided with a plurality of holes and the pattern of the plate electrode is transferred to the tool electrode. Electric discharges are then caused between a workpiece and the tool electrode having the transferred pattern. During the electro discharge machining, the relative distance between the tool electrode and the plate electrode or the workpiece is changed at a frequency and in an amplitude as desired, and discharge pulse output is controlled in synchronization with the change in the relative distance between the tool electrode and the plate electrode or the workpiece.
Multiple hole groups each including a plurality of holes are provided in a thin plate electrode. A tool electrode is machined sequentially using the multiple hole groups in the plate electrode, so that the transfer accuracy is increased by the use of the thin plate electrode, and a tool electrode having a necessary length for the machining is produced.
A micro electro discharge machining apparatus according to the present invention includes a tool electrode, a circuit for generating pulsed electric discharge between the tool electrode and a workpiece, a device for positioning the workpiece in an XY-plane, a device for positioning the tool electrode in the Z-direction orthogonal to the XY-plane, a vibration member for changing the relative distance between the tool electrode and the workpiece at a frequency and in an amplitude as desired, and a device for controlling a discharge pulse in synchronization with the change in the relative distance between the tool electrode and the workpiece.
A plate electrode provided with a plurality of holes may be used to produce a tool electrode.
When a plate electrode provided with multiple hole groups each including a plurality of holes is used to produce a tool electrode, the transfer accuracy is more improved.
While novel features of the invention are set forth in the preceding, the invention, both as to organization and content, can be further understood and appreciated, along with other objects and features thereof, from the following detailed description and examples when taken in conjunction with the attached drawings.